Automobiles are an indispensable part of everyday life to many people. Coupled with the existence of automobiles is a requirement for an energy source to provide the motive force to the wheels of the automobiles. The vast majority of the vehicles currently on the road require gasoline or diesel fuel as this energy source. As a result, vehicles are equipped with fuel tanks that must be filled periodically as the fuel is depleted. During a conventional or standard fueling operation, incoming fuel displaces fuel vapor from the head space of the fuel tank. The displaced fuel vapor exits through the filler pipe of the vehicle into the atmosphere.
The Environmental Protection Agency and various state agencies including the California Air Resources Board (CARB) have been proposing various regulations to limit the amount of fuel vapor released into the atmosphere during the fueling of a motor vehicle. While this legislation has not directly impacted many fueling environments, some states, such as California, have enacted much more stringent rules and regulations governing the amount of fuel vapor that can be released.
As a result of the rulemaking at the state level, fuel dispenser manufacturers began equipping fuel dispensers with vapor recovery systems that collect fuel vapor vented from the fuel tank filler pipe during the fueling operation and transfer the vapor to a fuel storage tank. The early vapor recovery systems were balance systems that had a boot around the nozzle. The boot formed a seal around the filler neck aperture. In balance systems, as fuel is introduced into the fuel tank, the displaced vapors are trapped by the boot and conveyed to a vapor recovery line in the hose. This arrangement relies on the pressure of the displaced vapors to move the vapors to the fuel storage tank.
A subsequently developed system added a vacuum pump to the vapor recovery line to assist in the recovery of vapor. The vacuum pump actively draws the displaced vapors through holes in the nozzle to a vapor recovery line in the hose. This arrangement may allow the boot to be eliminated, because the vacuum pump catches the vapors before they can escape. Two primary variations exist for the vacuum assist vapor recovery systems. The first variation is a constant speed pump with a proportional valve, and the second variation is a variable speed pump with an on/off valve.
Recently, onboard, or vehicle-carried, fuel vapor recovery and storage systems (commonly referred to as onboard refueling vapor recovery or ORVR) have been developed in which the head space in the vehicle fuel tank is vented through a charcoal-filled canister so that the vapor is absorbed by the charcoal. Subsequently, the fuel vapor is withdrawn from the canister into the engine intake manifold for mixture and combustion with the normal fuel and air mixture.
A problem arises when an ORVR vehicle is fueled at a fuel dispenser having a vacuum assist vapor recovery system. Specifically, the two vapor recovery systems compete against one another for the recovery of the vapors. This competition wastes energy, increases wear and tear on the vacuum pump, and may ingest excessive air into the underground storage tank. Specifically, when a vacuum assist vapor recovery system operates concurrently with an ORVR system, the fueling environment's vapor recovery system will draw air (without fuel vapors) into the vapor return line. This air is conveyed to the underground fuel storage tank. This air then mixes with the fuel in the tank and expands, causing pressure levels within the underground tank to increase. As the pressure level increases, a pressure valve may release some of the vapor within the tank to prevent over-pressurization. This may begin a cycle of tank “breathing.”
The problems associated with the competition between the two systems have been recognized and discussed in “Estimated Hydrocarbon Emissions of Phase II and Onboard Vapor Recovery Systems” dated Apr. 12, 1994, amended May 24, 1994, by the California Air Resources Board (CARB). That paper suggests the use of a “smart” interface on a nozzle to detect an ORVR vehicle and close one vapor intake valve on the nozzle when an ORVR vehicle is being fueled. By closing the valve on the nozzle, no air is drawn into the underground tank.
Another solution, introduced by the assignee of the present invention, is to use a pressure sensor within the vapor return line to determine if an ORVR vehicle is present. If an ORVR vehicle is detected, the vapor recovery system is adjusted so that a small amount of air is drawn in through the vapor recovery system in the belief that this small amount of air may expand to approximately the volume of fuel that was dispensed and minimize the risk of “breathing” by the underground storage tank. This approach is memorialized in U.S. Pat. Nos. 5,782,275 and 5,992,395, both of which are hereby incorporated by reference in their entireties.
Another problem has been discovered when ORVR vehicles are fueled at balance-type vapor recovery fuel dispensers where a seal is formed between the nozzle and the vehicle fuel tank. Specifically, the ORVR system of the vehicle may create a negative pressure that draws vapors from the underground storage tank into the fuel tank of the vehicle and may reduce pressure levels in the underground storage tank. Alternatively, in vacuum assist vapor recovery systems, the negative pressure will not draw vapors from the underground storage tank, but will gradually increase the vacuum in the fill pipe of the fuel tank. This increase in the negative pressure may cause a nuisance shut-off where the nozzle valve prematurely closes, stopping the delivery of fuel. To counteract these nuisance shut-offs, some manufacturers have begun introducing apertures in the boot by perforating the boot in one or two locations. These apertures allow atmospheric air into the boot and fuel tank to prevent the development of a negative pressure at the nozzle. However, when the vehicle being fueled is not an ORVR vehicle, the apertures allow vapor-laden air to escape into the atmosphere, defeating the purpose of the vapor recovery systems.
Thus, there is a need for additional solutions that allow the fuel dispenser to sense ORVR vehicles and take corrective measures to prevent over-pressurization of the underground storage tank, eliminate nuisance shut-offs, and allow for efficient vapor recovery to comply with the appropriate state and federal regulations.